Have you been wondering why that Snickers bar just doesn't satisfy like it used to?

The maker of confectionery such as Snickers, Mars, Twix, and M&M's has followed the lead of other chocolate producers and trimmed the size of its products but without cutting the price.

It blames continuing commodity cost increases and a need to help tackle obesity by reducing the calorie content of chocolate products.

Mars New Zealand general manager Gerry Lynch confirmed prices of smaller fun-size units, confectionery bars, and larger bags would remain the same, even though their weight had been reduced.

The company had absorbed prices during the past few years but that could not continue so downsizing was chosen over price increases, he said.

Prices would need to rise by up to 15 per cent to cover cost increases and that was unrealistic.

"We want to remain competitive and a lot of our competitors have reduced their sizes. If we start passing on commodity prices and currency changes then we become unaffordable for the consumer," Mr Lynch said.

Each smaller fun-size bar has been reduced to 100 calories per unit, while single bars such as Mars and Twix had been cut so they were about 250 calories.

Mars bars had been cut from 60 grams to 53g, while Twix bars were now 53g rather than 58g.

Bags of M&M's have been cut from 250g to 200g, bags of Pods 180g to 160g, while Malteaser bags went from 165g to 140g.

Smaller serving sizes would also encourage people to eat smaller quantities.

"But we're not going to hide behind the obesity issue and claim that's the reason we're doing this. There is a financial aspect to this where we can only absorb costs for so long before we have to pass some of that on," he said.

Reducing the weight of products was happening across various grocery categories, he said.

Chocolate giant Cadbury has come under fire from consumers after cutting the size of its Dairy Milk blocks from 250g to 200g, and changed the recipe.